# Heater Controls

**URL:** <https://community.cartalk.com/t/heater-controls/60411>\
**Category:** Maintenance/Repairs\
**Tags:** chevrolet, classic, caprice\
**Created:** [January 24, 2011, 6:36pm UTC](https://community.cartalk.com/t/heater-controls/60411 "2011-01-24T18:36:56Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![edb1961](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/edb1961/32/122_2.png) [@edb1961](https://community.cartalk.com/u/edb1961)\
**Post date:** [January 24, 2011, 6:36pm UTC](https://community.cartalk.com/t/heater-controls/60411/1 "2011-01-24T18:36:56Z")

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For the last couple of years, I’ve noticed the air flow changes from the floor to the defroster under hard acceleration. Not a big deal. This morning (7 degrees) the airflow was changing under light to moderate acceleration.  
  
  
  
 It’s a vacuum problem, but is there anything in particular I should be looking at? The car is running fine, no issues with stalling or hesitation.  
  
  
  
 Thanks in advance,  
  
  
  
 Ed B.

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**Author:** ![Cougar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/cougar/32/21348_2.png) [@Cougar](https://community.cartalk.com/u/Cougar)\
**Post date:** [January 24, 2011, 10:14pm UTC](https://community.cartalk.com/t/heater-controls/60411/2 "2011-01-24T22:14:36Z")

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There should be a vacuum reservoir tank under the hood somewhere. Its job is to supply vacuum to the vent doors while the engine is under acceleration and has a low vacuum level. There may be a crack to the tank or restrictor problem.

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**Author:** ![realbinky](https://avatars.discourse-cdn.com/v4/letter/r/a87d85/32.png) [@realbinky](https://community.cartalk.com/u/realbinky)\
**Post date:** [January 24, 2011, 10:40pm UTC](https://community.cartalk.com/t/heater-controls/60411/3 "2011-01-24T22:40:55Z")

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The control itself could be leaking. This happened in my Ranger. In my Olds Silhouette, it was a mechanical control, and the silicone manifold was leaking. It’s a minor leak, since it is only under hard accel (the cold shrinks components, so the leak could be worse)

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**Author:** ![BustedKnuckles](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bustedknuckles/32/25_2.png) [@BustedKnuckles](https://community.cartalk.com/u/BustedKnuckles)\
**Post date:** [January 24, 2011, 11:29pm UTC](https://community.cartalk.com/t/heater-controls/60411/4 "2011-01-24T23:29:08Z")

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Most likely a bad check valve. The check valve is supposed to maintain vacuum in the climate control lines when the engine vacuum drops. Just another thing to look for.

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**Author:** ![edb1961](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/edb1961/32/122_2.png) [@edb1961](https://community.cartalk.com/u/edb1961)\
**Post date:** [January 25, 2011, 2:07pm UTC](https://community.cartalk.com/t/heater-controls/60411/5 "2011-01-25T14:07:09Z")

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Thanks for the suggestions, I will have to crack open the Factory Service manual and see what’s where.

Ed B.